The women submitted monthly urine samples to assess pregnancy status, and their monthly cycle phases were calculated using a calendar-based method and compared between drinkers and nondrinkers.
During the study, 133 women became pregnant, and outcomes showed an effect of alcohol — the more alcohol a woman drank, the less chance she had of conceiving. “Among heavy drinkers, the probability of conceiving was 27.2%, rising to 41.3% in nondrinkers. Light and moderate drinkers both had about a 32% chance of conceiving,” Taylor says.
When the researchers looked at the effect of drinking alcohol during different phases of the menstrual cycle, they found that moderate and heavy drinking in the post-ovulation phase reduced the odds of conception by nearly half (44% and 49%, respectively), compared with nondrinkers. There was also some suggestion that heavy drinking before ovulation was also tied to reduced likelihood of conception.
How about binge drinking? Notably, each extra day of excessive intake over a short period was associated with a 19% reduction in conception around the time of ovulation and between ovulation and menstruation. But it didn’t seem to have an effect early in the cycle, before ovulation.
The researchers also found that the type of alcoholic beverage didn’t change the results.
“In addition, the study showed that the menstrual cycle lengths were the same for women in every drinking category, suggesting that drinking did not affect the hormones that regulate the length of the cycle,” says Christine Metz, PhD, a professor at the Feinstein Institutes for Medical Research in Manhasset, NY.
The authors think that part of the alcohol-conception connection may be disruptive changes in steroid hormones, particularly a surge in estradiol, a form of estrogen
“The increase in estrogen can result in irregular cycles, delayed ovulation, or anovulation. So couples could be trying to get pregnant at the wrong time in terms of ovulation,” Taylor says. “An increase in estrogen can also impact the timing of the window of opportunity in the lining of the uterus for implantation after fertilization.”
Experts are not exactly sure how a badly timed spike in estradiol might affect the odds of conception. While this is not clearly understood, it seems that the timing of heavy drinking may not only suppress ovulation, but may also suppress the ability to sustain an early pregnancy, notes Ali.